1. Field of the Invention
The present invention relates to an image forming apparatus including an image controlling unit, and a method of controlling an image quality.
2. Description of the Related Art
A related art image forming apparatus performs an image control in an image quality controlling mode. In the image quality control mode, an image controller of the related art image forming apparatus causes an optical writing unit to form test patterns on a surface of an image bearing member. An image density sensor of the related art image forming apparatus detects the image density of the test pattern so that the controller can control an image quality based on the detection result.
The image control is required to be performed at predetermined intervals, so the related art image forming apparatus performs the image control during a standby state until the power of the related art image forming apparatus is turned on or during an image forming operation at the timings of the predetermined intervals.
When the image control is performed during an image forming operation, test patterns are formed in an area or areas outside of an image forming area on the surface of an image bearing member so as to be used for detecting the density of the patterns. By performing the image control during the image forming operation, the related art image forming apparatus can reduce a system stopping time thereof.
However, areas that are located outside of an image forming area for forming test patterns have recently been reduced, and technologies for image control are becoming more accurate. For these reasons, it has become more difficult to form test patterns on such areas of the image bearing member during the image forming operation. The recent image controls, therefore, are performed while the related art image forming apparatus has stopped or interrupted the image forming operations.
When interrupting the image forming operations of the related art image forming apparatus, the previously performed image forming operations are required to be stopped in an orderly manner before starting the image controls. At the same time, a photoconductive element drive unit, a transfer member drive unit, and so forth are stopped. When the related art image forming apparatus employs an optical writing unit, a polygon motor drive unit and so forth are required to be stopped to stop the operations for image forming, and then it is required to reboot the operations for image control.
The above-described sequential operations are generally performed, because an adverse effect such as damage may be lessened to the related art image forming apparatus and the above-described drive units may have less complicated respective structures and functions. The above-described sequential operations, however, need to be stopped then it is required to reboot the above-described drive units, and that may cause the system stopping time to become longer.
To avoid the long system stopping time, there are some techniques that can form test patterns for image control while the related art image forming apparatus is interrupting the image forming operations without stopping the drive units of the related art image forming apparatus.
One technique provides a first method in which the image control is performed with the presently used image forming condition for the image forming operation.
Another technique provides a second method in which the image control is performed after changing the presently used image forming condition for the image forming operation to a test pattern forming condition for the image control, when these conditions are not identical.
In the first method, an image density control for determining an exposing condition and a development potential condition may be identical to the density detecting condition of the test pattern for the image control and the image forming condition for the image forming operation. Therefore, when the result data of the image control is applied to the image forming condition at a different linear velocity, it is required to correct the result data according to the conditions previously determined by each linear velocity or to detect respective densities of the test patterns for image control by each linear velocity.
However, when the result is corrected according to each of the previously determined conditions by each linear velocity, various corrections may be performed. For example, the various corrections are performed when the result of the image control with a low linear velocity is applied to the image forming condition with a high linear velocity or when the result of the image control with a high linear velocity is applied to the image forming condition with a low linear velocity. The various corrections of the former case are not always identically reversed to those of the latter case, and accumulated errors may arise in these cases.
Further, when the various corrections are used to control the image quality according to each linear velocity, the system stopping time for the image control may become long.
Furthermore, when the related art image forming apparatus has a separation mechanism in which photoconductive members other than a black image photoconductive element are separated from a transfer member when forming a black-and-white image, the image control may be performed two times. That is, the image control is performed for the black-and-white image while the separation mechanism separates the photoconductive elements other than the black image photoconductive element, and the image control is performed for the cyan, magenta, and yellow images while the separation mechanism causes contact of the photoconductive elements.
On the other hand, in the second method, when the drive units drive the respective units at different speeds for the image forming operation and the image control, the speeds may be changed when switching the operations between the image forming operation and the image control. When the speed is changed, a load may be given to the units in contact with each other. For example, such a load may be given to a cleaning blade and an image bearing member disposed in contact with each other. The load may also be given to each photoconductive element and a transfer belt in contact with each other. This can cause damage to and/or deterioration in the related art image forming apparatus.
Further, for the adjustments of image density sensors and image shift sensors, the image bearing members that include the photoconductive elements and the transfer belt may be rotated with the toner patterns thereon, and the image density sensors and the image shift sensors may detect and obtain data of the reflectivity of the toner patterns on the photoconductive elements and the transfer belt.
Unfortunately, the image bearing member and the transfer belt can be damaged due to abrasion and scratches, and thereby the reflectivity on the respective surfaces thereof may become uneven. Therefore, when the reflectivity is measured at a small portion of each surface of the photoconductive elements and the transfer belt, the result of the reflectivity may greatly differ from the actual reflectivity of an entire surface thereof. This can decrease the level of accuracy in detection by the sensors. For the above-described reasons, the reflectivity of the toner patterns formed on the photoconductive elements and the transfer member may be measured in a wide range of the areas, which may need a long time for measuring.